Dual clutches are used in motor vehicles for enabling power-shifting.
A dual clutch arrangement comprising a first partial clutch K1 and a second partial clutch K2 is disclosed, for instance, in EP 0 185 176 B1.
According to the arrangement in a dual clutch of the pre-cited type, both partial clutches K1 and K2 are open in the normal state (“normally open”) and are pressed to close through at least one actuating device. The actuating forces required to close the clutches are normally applied alternately and must be applied in the same direction. These actuating forces have then to be taken up by a support bearing arranged on the crankshaft or in the transmission. The forces resulting in such an arrangement can be seen in the diagram shown in FIG. 8. In this diagram, the partial clutch K1 is at first open, and the partial clutch K2 is at first closed. The total actuating force is therefore equal to the actuating force of the partial clutch K2. An overlapping shifting is then executed to close the partial clutch K1 and open the partial clutch K2. Accordingly, the actuating force of the partial clutch K1 increases and the actuating force of the partial clutch K2 decreases. The total actuating force, however, remains substantially unchanged. In the final state, the partial clutch K1 is closed and the partial clutch K2 is open. The total actuating force corresponds to the actuating force of the partial clutch K1. As can be seen in this diagram, the total actuating force remains substantially at the same level over the entire period of time.
According to the arrangement in an alternative embodiment of the dual clutch, the partial clutch K1 is closed in the normal state (“normally closed”) and is pressed open through at least one actuating device, while the partial clutch K2 is open in the normal state (“normally open”) and is pressed to close through at least one actuating device. Two different states result in such an arrangement: when the partial clutch K1 is closed and the partial clutch K2 is open, no actuating force is required. In contrast, to open the partial clutch K1 and close the partial clutch K2, two actuating forces are needed. In this case, the two actuating forces add up and produce a high axial force on the support bearing.
The forces resulting in such an arrangement can be seen in the diagram shown in FIG. 9. In this diagram, the partial clutch K1 is at first open, and the partial clutch K2 is at first closed. The total actuating force is therefore equal to the sum of the opening force of the partial clutch K1 and the closing force of the partial clutch K2. An overlapping shifting is then performed to close the partial clutch K1 and open the partial clutch K2. Accordingly, the actuating force of the partial clutch K1 is reduced to almost zero. In the final state, the partial clutch K1 is closed and the partial clutch K2 is open. The total actuating force again corresponds to the sum of the actuating forces of the partial clutches K1 and K2.
In case of use in trucks which can have a torque of up to 3300 to 3500 Nm, release forces of up to 12400 to 15000 N are produced. If it is desired to use a dual clutch in trucks, the crankshaft mounting or the transmission bearing of the arrangement described above would have to support twice the actuating force. Therefore, to avoid such a design of the mounting arrangement and also all concomitant modifications to the housing, it is desirable to minimize the sum of the two actuating forces.